Asymmetric synthesis and anti-protozoal activity of the 8,4'-oxyneolignans virolin, surinamensin and analogues

Modular Enantioselective Total Syntheses of the erythro-7,9-Dihydroxy- and 9-Hydroxy-7-Keto-8,4'-Oxyneolignans

A modular, enantioselective approach to access the bioactive 7,9-dihydroxy- and 9-hydroxy-7-keto-8,4'-oxyneolignans is disclosed, which employs stereoselective Mitsunobu reactions of enantiopure 2-aryl-1,3-dioxan-5-ols and functionalized phenols. The enantiopure dioxanols are prepared through Sharpless asymmetric dihydroxylation of protected coniferyl or sinapyl alcohols and subsequent benzylidene acetal formation. Through a mix-and-match coupling approach, six of the eight possible erythro-7,9-dihydroxy-8,4'-oxyneolignan enantiomeric natural products (bearing a C-1' hydroxypropyl chain) were generated following sequential deprotection. Subsequent benzylic oxidation afforded the 7-keto-derivatives, resulting in enantioselective syntheses of each enantiomer of the natural products asprenol B and icariol A1.

Insights into the inhibitory activities of neolignans and diarylnonanoid derivatives from nutmeg (Myristica fragrans Houtt.) seeds on soluble epoxide hydrolase using in vitro and in silico approaches

Two new neolignans, myrifralignans F-G (14 and 18), four new diarylnonanoid derivatives, myrifragranones A-D (21-24), and 18 known compounds were isolated and structurally elucidated from nutmeg (Myristica fragrans Houtt.) seeds. The absolute configurations of these secondary metabolites were determined using the electronic circular dichroism technique. The inhibitory potential of these isolated compounds on soluble epoxide hydrolase (sEH) was investigated for the first time. Among them, malabaricones B and C (19 and 20) and four new compounds 21-24 displayed inhibitory activities against sEH, with IC50 values ranging from 14.24 to 46.35 µM. Additionally, the binding mechanism, key binding interactions, stability, and dynamic behaviour of the active compounds with the sEH enzyme were analysed using in silico molecular docking and dynamics simulations. Our findings suggest that nutmeg could become a promising natural source for discovering and developing new sEH inhibitors.

Rapid determination of the relative configuration of diverse 8,4'-oxyneolignans by NMR analysis: Retrospective studies, improvement and structural revision

The characteristic 1H NMR signals (H-7 and H2-9) are significant parameters that have been widely used to assess the relative configuration of H-7 and H-8 of 8,4'-oxyneolignans. However, many usual 8,4'-oxyneolignans cannot be accurately determined by existing NMR methods and no research considering their limitations was performed until now. In this study, the application scope of NMR methods was comprehensively studied and the ΔδH9a-H9b methods have been extended to solve the majority of configuration determination difficulties. The accuracy of extended NMR methods was verified by anisotropic NMR (RCSA measurements), NMR calculation and diverse statistical analysis (MAEΔΔδ, CP3 and DP4+). Furthermore, the theoretical conformational analysis was performed to investigate the inherent limitations of existing NMR methods. This study could provide a valuable reference for determining the relative configuration of H-7 and H-8 in 8,4'-oxyneolignans and the relative configuration of 23 recently reported 8,4'-oxyneolignan derivatives should be reassigned as well.

(-)-5-Demethoxygrandisin B a New Lignan from Virola surinamensis (Rol.) Warb. Leaves: Evaluation of the Leishmanicidal Activity by In Vitro and In Silico Approaches

Leishmaniasis is a complex disease caused by infection with different Leishmania parasites. The number of medications used for its treatment is still limited and the discovery of new drugs is a valuable approach. In this context, here we describe the in vitro leishmanicidal activity and the in silico interaction between trypanothione reductase (TryR) and (-)-5-demethoxygrandisin B from the leaves of Virola surinamensis (Rol.) Warb. The compound (-)-5-demethoxygrandisin B was isolated from V. surinamensis leaves, a plant found in the Brazilian Amazon, and it was characterized as (7R,8S,7'R,8'S)-3,4,5,3',4'-pentamethoxy-7,7'-epoxylignan. In vitro antileishmanial activity was examined against Leishmania amazonensis, covering both promastigote and intracellular amastigote phases. Cytotoxicity and nitrite production were gauged using BALB/c peritoneal macrophages. Moreover, transmission electron microscopy was applied to probe ultrastructural alterations, and flow cytometry assessed the shifts in the mitochondrial membrane potential. In silico methods such as molecular docking and molecular dynamics assessed the interaction between the most stable configuration of (-)-5-demethoxygrandisin B and TryR from L. infantum (PDB ID 2JK6). As a result, the (-)-5-demethoxygrandisin B was active against promastigote (IC50 7.0 µM) and intracellular amastigote (IC50 26.04 µM) forms of L. amazonensis, with acceptable selectivity indexes. (-)-5-demethoxygrandisin B caused ultrastructural changes in promastigotes, including mitochondrial swelling, altered kDNA patterns, vacuoles, vesicular structures, autophagosomes, and enlarged flagellar pockets. It reduced the mitochondria membrane potential and formed bonds with important residues in the TryR enzyme. The molecular dynamics simulations showed stability and favorable interaction with TryR. The compound targets L. amazonensis mitochondria via TryR enzyme inhibition.

Use of Natural Products in Leishmaniasis Chemotherapy: An Overview

Leishmaniasis is an infectious parasitic disease that is caused by protozoa of the genus Leishmania, a member of the Trypanosomatidae family. Leishmaniasis is classified by the World Health Organization as a neglected tropical disease that is responsible for millions of deaths worldwide. Although there are many possible treatments for leishmaniasis, these treatments remain mostly ineffective, expensive, and long treatment, as well as causing side effects and leading to the development of resistance. For novel and effective treatments to combat leishmaniasis, many research groups have sought to utilize natural products. In addition to exhibiting potential as therapeutic compounds, natural products may also contribute to the development of new drugs based on their chemical structures. This review presents the most promising natural products, including crude extracts and isolated compounds, employed against Leishmania spp.

Vanadium-Catalyzed Selective Oxidative Homocoupling of Alkenyl Phenols to Synthesize Lignan Analogs

The oxidative homocoupling of para-alkenyl phenols and subsequent trapping of the resulting quinone methide with a variety of oxygen and nitrogen nucleophiles was achieved. Both β-β and β-O coupling isomers can be synthesized via either C-C coupling and two nucleophilic additions of one water molecule (β-β isomer) or C-O coupling followed by one nucleophilic addition of a water molecule (β-O isomer), respectively. Selectivity between these outcomes was achieved by leveraging understanding of the mechanism. Specifically, a qualitative predictive model for the selectivity of the coupling was formulated based on catalyst electronics, solvent polarity, and concentration.

Recent Advances in the Discovery of Novel Antiprotozoal Agents

Parasitic diseases have serious health, social, and economic impacts, especially in the tropical regions of the world. Diseases caused by protozoan parasites are responsible for considerable mortality and morbidity, affecting more than 500 million people worldwide. Globally, the burden of protozoan diseases is increasing and is been exacerbated because of a lack of effective medication due to the drug resistance and toxicity of current antiprotozoal agents. These limitations have prompted many researchers to search for new drugs against protozoan parasites. In this review, we have compiled the latest information (2012-2017) on the structures and pharmacological activities of newly developed organic compounds against five major protozoan diseases, giardiasis, leishmaniasis, malaria, trichomoniasis, and trypanosomiasis, with the aim of showing recent advances in the discovery of new antiprotozoal drugs.

Stereoselective Total Synthesis of (+)-Aristolactam GI

Aristolactams are an important subgroup of aporphinoids, which all share a common phenanthrene chromophore motif that is thought to be responsible for the range of interesting physicochemical and biological properties exhibited by these compounds. Among all of the aristolactams discovered, (+)-aristolactam GI displays a unique structural feature of having the aristolactam scaffold linked via a benzodioxane ring to a phenyl propanoid unit, resulting in the compound being an aporphinoid-lignan hybrid. The synthesis of (+)-aristolactam GI was achieved first by synthesis of an orthogonally protected aristolactam, which was prepared using a Suzuki/aldol cascade to convert a differentially protected isoindolin-1-one to the required phenanthrene. The required enantiopure phenyl propanoid unit was prepared from readily available ( R)-methyl lactate. A selective Mitsunobu reaction was used to combine these two key fragments, prior to the formation of the linking benzodioxane in the final step. The absolute stereochemistry of the natural product was confirmed to be 7' S, 8' S.

Modular Synthesis and Biological Investigation of 5-Hydroxymethyl Dibenzyl Butyrolactones and Related Lignans

Dibenzyl butyrolactone lignans are well known for their excellent biological properties, particularly for their notable anti-proliferative activities. Herein we report a novel, efficient, convergent synthesis of dibenzyl butyrolactone lignans utilizing the acyl-Claisen rearrangement to stereoselectively prepare a key intermediate. The reported synthetic route enables the modification of these lignans to give rise to 5-hydroxymethyl derivatives of these lignans. The biological activities of these analogues were assessed, with derivatives showing an excellent cytotoxic profile which resulted in programmed cell death of Jurkat T-leukemia cells with less than 2% of the incubated cells entering a necrotic cell death pathway.

Lignans: A Chemometric Analysis

The physicochemical properties of classical lignans, neolignans, flavonolignans and carbohydrate-lignan conjugates (CLCs) were analysed to assess their ADMET profiles and establish if these compounds are lead-like/drug-like and thus have potential to be or act as leads in the development of future therapeutics. It was found that while no studied compounds were lead-like, a very large proportion (>75%) fulfilled all the requirements to be deemed as present in drug-like space and almost all compounds studied were in the known drug space. Principal component analysis was an effective technique that enabled the investigation of the relationship between the studied molecular descriptors and was able to separate the lignans from their sugar derivatives and flavonolignans, primarily according to the parameters that are considered when defining chemical space (i.e., number of hydrogen bond donors, acceptors, rotatable bonds, polar surface area and molecular weight). These results indicate that while CLCs and flavonolignans are less drug-like, lignans show a particularly high level of drug-likeness, an observation that coupled with their potent biological activities, demands future pursuit into their potential for use as therapeutics.

HM, Nair VA. Anti selective glycolate aldol reactions of (S)-4-isopropyl-1-[(R)-1-phenylethyl]imidazolidin-2-one: application towards the asymmetric synthesis of 8-4′-oxyneolignans

The anti selective glycolate aldol reactions of (S)-4-isopropyl-1-[(R)-1-phenylethyl]imidazolidin-2-one auxiliary have been standardized with high yields and excellent diastereoselectivities on various substituted aryl, allyl and alkyl aldehydes.